The piston of a hydraulic actuator is generally provided with a seal assembly to prevent leakage of hydraulic fluid past the piston. Such seal assemblies often comprise a relatively hard primary or dynamic sealing ring that is backed up by a relatively softer secondary or static sealing ring. Moreover, such seal assemblies are often provided with back up rings made of relatively hard material, for example, polyamide.
However, a problem exists in that known back up rings are often displaced incident to assembly of the piston into the cylinder bore. The back up rings may be forced out of the piston gland upon assembly with a cylinder or may fall out of the piston gland before the piston is telescoped into the cylinder. Moreover, known back up rings are susceptible of improper installation in the piston gland.
The aforesaid problems are solved, in accordance with a preferred constructed embodiment of the present invention, by providing a mechanical interlock between either the primary or secondary piston sealing ring and the back up rings. Stated in another manner, a locking arrangement between the back up rings and seal elements in the form of a mechanical interface between the back up rings and one or more sealing elements of the piston ring assembly precludes inadvertent disassembly as well as improper installation of the back up rings. The locking feature can be arranged to provide similar benefits in bi-directional and uni-directional rod seal assemblies.